test: make module test pass with NODE_PENDING_DEPRECATION

Some people set the `NODE_PENDING_DEPRECATION` environment variable
globally. This makes the test added in 115f0f5
pass when that is the case.

Refs: nodejs#26823

Author: addaleax

test/sequential/test-module-loading.js

@@ -29,7 +29,8 @@ const path = require('path');
 
 const backslash = /\\/g;
 
-process.on('warning', common.mustNotCall());
+if (!process.env.NODE_PENDING_DEPRECATION)
+  process.on('warning', common.mustNotCall());
 
 console.error('load test-module-loading.js');